Field of the Invention
The invention relates to a method for determining a position in accordance with the measurement signal of a position sensor, in particular for the use of the position sensor in the case of an electromechanical actuator for gas exchange valves of an internal combustion engine.
Accurate determination of the position of the gas exchange valve is the basis for low-noise and substantially wear-free operation of an electromechanical actuator, which is for example intended to control the movement of gas exchange valves of an internal combustion engine. Such electromechanical actuators are known, for example, from U.S. Pat. No. 5,752,478 (see Japanese application JP 31394/95 and European application EP 0 724 067 A1).
Position sensors, which comprise a magnetoresistive element and a permanent magnet which can be displaced in relation to the magnetoresistive element, are used to detect positions in the case, in particular, of electromechanical actuators. Magnetoresistive elements, in particular so-called Giant Magneto-Resistive (GMR) elements, produce a measurement signal which depends on the direction of the magnetic field acting on them. In the case of a linear movement of the permanent magnet to the magnetoresistive element, the measurement signal of the position sensor essentially has a cosinusoidal profile.
The relationship between the measurement signal of the position sensor and the associated position is determined by measurements on a reference position sensor, and then stored in the form of a characteristic map, e.g. as tables in control units which determine the position from the characteristic in accordance with the measurement signal of the series position sensor. Errors may thereby possibly occur in the determination of the position, firstly through inaccuracies in the arrangement of the permanent magnet on the object whose position is to be detected, with respect to the arrangement of the magnetoresistive element, secondly through inaccuracies in the arrangement of the sensor element, thirdly because of tolerances in the manufacture of the position sensors, and fourthly through the effect of perturbations such as the temperature of the sensor element.
It is accordingly an object of the invention to provide a method for determining a position in accordance with the measurement signal of a position sensor, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which ensures accurate and reliable determination of the position.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of determining a position in dependence on a measurement signal of a position sensor, the position sensor having a sensor element and a transmitter part displaceable between a first end position and a second end position, and the measurement signal having an extreme value between the first end position and the second end position. The method comprises the following method steps:
determining actual values of the measurement signal in a first end position and a second end position;
determining an extreme value of the measurement signal between the first end position and the second end position; and
determining a position in dependence on a current actual value of the measurement signal, the extreme value and the actual values in the first end position and the second end position.
In accordance with an added feature of the invention, a parameter for an axial offset between the transmitter part and the sensor element is determined in dependence on the extreme value of the measurement signal and the actual values of the measurement signal in the first end position and in the second end position, and the position is determined in dependence on the parameter.
In accordance with an additional feature of the invention, the position sensor is disposed to detect the position of an electromechanical actuator, and the parameter is determined during a starting operation of the actuator.
In accordance with another feature of the invention, there are determined a gain value and an offset value in dependence on the parameter for the axial offset, the extreme value of the measurement signal and the actual values in the first end position and the second end position, and the respective current measurement signal is corrected in dependence on the gain value and the offset value.
In accordance with a further feature of the invention, the gain value and the offset value are determined when a predetermined period of time has elapsed during the operation of the position sensor, and/or a quantity characterizing a temperature of the position sensor has changed by a predetermined threshold value, and/or an error of the position in the end positions has been detected.
In accordance with again an added feature of the invention, the method encompasses determining the position, in dependence on the corrected current measurement signal, from a characteristic and the parameter for the axial offset.
In accordance with again another feature of the invention, the parameter for the axial offset is a corrected setpoint value of the measurement signal in the first end position or the second end position.
In accordance with a concomitant feature of the invention, the extreme value of the measurement signal is chosen as the maximum value.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for determining a position with a measurement signal of a position sensor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.